Depending on their wavelength, UV rays are divided in UV-A rays (320-400 nm) and UV-B rays (280-320 nm). The harmful effect, in particular the occurrence of sunburn (erythema), increases not only with the duration of exposure but also with decreasing wavelength and is thus significantly more strongly marked in the case of UV-B radiation than in the case of UV-A radiation. Since erythemas can occur even after short exposure to the sun, in some cases after 20-30 minutes, efficient protection against this radiation is of particular importance.
For this area of UV protection, a number of UV-B absorbers are already known from the prior art. Examples mentioned are camphor derivatives, salicylic acid derivatives, benzophenones, cinnamates, benzimidazoles and triazines. One example of benzylidene-.gamma.-butyrolactones is described in European Patent Application EP-A 44970. These are compounds of the formula ##STR1##
in which
R is a C.sub.1 -C.sub.15 -alkyl radical, branched or unbranched, phenyl or benzyl. PA1 R is hydrogen or C.sub.1 -C.sub.6 -alkyl or cycloalkyl, and PA1 R.sup.1 to R.sup.5 independently of one another are hydrogen, but at most 4, are hydrogen at the same time, or C.sub.1 -C.sub.8 -alkyl or cycloalkyl, and also R.sup.1 /R.sup.2 and/or R.sup.3 /R.sup.4 can form a carbocyclic ring having from 5 to 7 ring atoms.
However, all of these compounds have the disadvantages that they are either in the form of a solid and thus have only limited solubility in the cosmetic preparations, exhibit only low absorption or have photostability which does not meet the necessary criteria and are thus unsatisfactory.